The present invention relates to a novel camptothecin derivative having enhanced antitumor activities. More particularly, the present invention relates to a novel camptothecin derivative which is prepared by combining an aminoalkoxy- or hydroxyalkoxy-camptothecin compound with a polysaccharide having carboxyl groups via an amino acid or a peptide, and a process for preparing the same. The camptothecin derivatives of the present invention can be delivered into a target region of the patient selectively and in much amount, so that they can show desired pharmacological activities at the desired region of the patient. Therefore, the antitumor activities of the camptothecin compounds are enormously enhanced and their side effects can be reduced, and hence, the camptothecin derivatives of the present invention are extremely useful as a medicaments.
Camptothecin is one plant alkaloids, and has the following formula: 
and it has been known to show antileukemic and antitumor activities, and one camptothecin derivative, irinotecan hydrochloride {CPT-11, 7-ethyl-1-[4-(piperidino)-1-piperidino]carbonyloxycamptothecin}, has already been put on the market. However, CPT-11 shows potent antitumor activities in clinical use but also shows severe toxicity like other antitumor agents, so that CPT-11 has been restricted in its therapeutic use [cf. Cancer and Chemotherapy, vol. 21, p. 709 (1994)].
There have been synthesized various camptothecin compounds, and it has been reported that these camptothecin compounds show antitumor activities (Japanese Patent First Publication (Kokai) Nos. 279891/1989, 222048/1993, 87746/1994, 228141/1994, and Japanese Patent First Publication (Kohyo) Nos. 503505/1992, 502017/1992).
On the other hand, in order to enhance antitumor activities and also to reduce the side effects thereof as low as possible, these compounds having such severe side effects have been studied as to a kind of drug delivery system therefor, by which a necessary amount of a drug is selectively delivered into a target tissue. Especially, in the chemotherapy of cancers, it is a serious problem that there is no significant difference between tumor cells and normal cells in sensitivity against anticancer agents, and many studies on targeting-type drug delivery system for anticancer agents have been done in order to selectively deliver an anticancer agent into a cancer-bearing region, for example, doxorubicin-polysaccharide complex (WO 94/19376), doxorubicin-inclusive liposome (Enhancement of effects of anticancer agents and targeting therapy, p. 227 (1987), published by Science Forum Ltd.), dextran-binding mitomycin (Enhancement of effects of anticancer agents and targeting therapy, p. 278 (1987), published by Science Forum Ltd.).
As explained above, camptothecin compounds show excellent anti-tumor activities and are very useful as a medicament but they are strictly restricted in clinical use because of their severe side effects. Thus, it is desired to develop a new camptothecin derivative wherein the excellent pharmacological activities of camptothecin compounds are duly retained but undesirable severe side effects are suppressed.
Under the above mentioned circumstances, the present inventors have intensively studied in order to obtain an excellent camptothecin derivative without the drawback of the conventional camptothecin compounds by utilizing the techniques of the above mentioned drug delivery system, and finally have found that a novel camptothecin derivative having desired pharmacological effects can be obtained by combining a camptothecin compound having a reactive group with a polysaccharide having carboxyl groups via an amino acid or a peptide, and have accomplished the present invention.
An object of the present invention is to provide a novel camptothecin derivative comprising the camptothecin compound [I] bound to a polysaccharide having carboxyl groups via an amino acid or a peptide, which has enhanced antitumor activities with less side effects.
Another object of the present invention is to provide a process for preparing these camptothecin derivative.
The compound of the present invention is a camptothecin derivative comprising a camptothecin compound having an aminoalkoxy group or a hydroxyalkoxy group, represented by the formula [I]: 
wherein R1, R2, R3, R4 and R5 are
(A) among R1, R2, R3, R4 and R5, two groups being adjacent each other combine to form an alkylene group, or both are a hydrogen atom, and one of the remaining three groups of R1, R2, R3, R4 and R5 is a group of the formula: xe2x80x94Xn-Alkm-R6, and the other two groups are a hydrogen atom, an alkyl group or a halogen atom, or
(B) among R1, R2, R3, R4 and R5, two groups being adjacent each other combine to form an alkylene group, and one of the carbon atoms of said alkylene group is substituted by a group of the formula: xe2x80x94Xn-Alkm-R6, and the remaining three groups of R1, R2, R3, R4 and R5 are a hydrogen atom, an alkyl group or a halogen atom, and
one or two methylene groups of the alkylene group in (A) or (B) may optionally be replaced by xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94 or xe2x80x94NHxe2x80x94,
X is xe2x80x94Oxe2x80x94 or xe2x80x94NHxe2x80x94,
Alk is an alkylene group,
R6 is xe2x80x94NH2, a group of the formula: 
xe2x80x83or xe2x80x94OH,
m and n are both 0 or 1, or m is 1 and n is 0,
which camptothecin compound is bound to a polysaccharide having carboxyl groups via an amino acid or a peptide. The camptothecin derivative of the present invention shows extremely potent antitumor activities but show low toxicity.
The camptothecin derivative of the present invention includes compounds which are prepared by combining the camptothecin compound [I] with a polysaccharide having carboxyl groups via an amino acid or a peptide. For example, such camptothecin derivatives may be prepared by combining a part or all of the carboxyl groups of an amino acid or a peptide with R6 of the compound [I] through acid-amide or ester bonds, followed by combining a part or all of the carboxyl groups of a polysaccharide with amino groups of said amino acid or said peptide through acid-amide bonds. More particularly, the camptothecin derivative of the present invention includes compounds which are prepared by combining the C-terminal carboxyl group of an amino acid or a peptide with R6 of the compound [I] through an acid-amide or ester bond, followed by combining a part or all of the carboxyl groups of a polysaccharide with the N-terminal amino group of said amino acid or said peptide through acid-amide bonds.
Each substituent of the compound of the formula [I] of the present invention is explained below.
The alkylene group in the definition (A) formed by combining adjacent two groups of R1, R2, R3, R4 and R5 each other, wherein one or two methylene groups may optionally be replaced by xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94 or xe2x80x94NHxe2x80x94, is formed by combining each other two substituents at 7- and 9-positions, 9- and 10-positions, 10- and 11-positions, or 11- and 12-positions of the formula [I], and the alkylene group includes a straight chain or branched chain alkylene group having 2 to 6 carbon atoms, for example, ethylene, trimethylene, tetramethylene, pentamethylene, hexamethylene, methylmethylene, methylethylene, methyltrimethylene, etc.
The above alkylene group wherein one of the methylene groups is replaced by xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94 or xe2x80x94NHxe2x80x94 includes an alkylene group wherein a methylene group at the end or at any position other than the end is replaced by xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94 or xe2x80x94NHxe2x80x94. For example, such alkylene group includes an alkyleneoxy group represented by the formula: xe2x80x94O-Alkxe2x80x2-(Alkxe2x80x2 is an alkylene group, hereinafter, the same) such as methyleneoxy, ethyleneoxy, trimethyleneoxy, tetramethyleneoxy, methylethyleneoxy; an alkyleneamino group represented by the formula: xe2x80x94NH-Alkxe2x80x2- such as methyleneamino, ethyleneamino, trimethyleneamino, tetramethyleneamino, methylethylene-amino; an alkylenethio group represented by the formula: xe2x80x94S-Alkxe2x80x2- such as methylenethio, ethylenethio, trimethylenethio, tetramethylenethio, methylethylenethio; an alkyleneoxyalkyl group represented by the formula: -Alkxe2x80x2-O-Alkxe2x80x2- such as methyleneoxymethyl, ethyleneoxymethyl, trimethyleneoxymethyl, methylethyleneoxymethyl; an alkyleneaminoalkyl group represented by the formula: -Alkxe2x80x2-NH-Alkxe2x80x2- such as methyleneaminomethyl, ethyleneaminomethyl, trimethyleneaminomethyl, methylethyleneaminomethyl; an alkylenethioalkyl group represented by the formula: -Alkxe2x80x2-S-Alkxe2x80x2- such as methylenethiomethyl, ethylenethiomethyl, trimethylenethiomethyl, methylethylenethiomethyl, and the like.
The above alkylene group wherein two methylene groups are replaced by xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94 or xe2x80x94NHxe2x80x94 includes an alkylene group wherein two methylene groups at the ends or at positions other than the ends are replaced by xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94 or xe2x80x94NHxe2x80x94. For example, such alkylene group includes an alkylenedioxy group represented by the formula: xe2x80x94O-Alkxe2x80x2-Oxe2x80x94 such as methylenedioxy, ethylenedioxy, trimethylenedioxy, tetramethylenedioxy, methylethylenedioxy; an alkylenediamino group represented by the formula: xe2x80x94NH-Alkxe2x80x2-NHxe2x80x94 such as methylenediamino, ethylenediamino, trimethylenediamino, tetramethylenediamino, methylethylenediamino; an alkylenedithio group represented by the formula: xe2x80x94S-Alkxe2x80x2-Sxe2x80x94 such as methylenedithio, ethylenedithio, trimethylenedithio, tetramethylenedithio, methylethylenedithio, and the like.
The Alk in the group of the formula: xe2x80x94Xn-Alkm-R6 includes a straight chain or branched chain alkylene group having 1 to 6 carbon atoms, for example, methylene, ethylene, trimethylene, tetramethylene, pentamethylene, hexamethylene, methylethylene, methyltrimethylene, etc. The group of the formula: xe2x80x94Xn-Alkm-R6 is, for example, an aminoalkyloxy group (e.g. aminoethyloxy, aminopropyloxy), a piperazinylalkyloxy group (e.g. piperazinylethyloxy, piperazinylpropyloxy, piperazinylbutyloxy, piperazinylpentyloxy), a hydroxyalkyloxy group (e.g. hydroxyethyloxy, hydroxypropyloxy, hydroxybutyloxy, hydroxypentyloxy), an aminoalkylamino group (e.g. aminoethylamino, aminopropylamino, aminobutylamino, aminopentylamino), a piperazinylalkylamino group (e.g. piperazinylethylamino, piperazinylpropylamino, piperazinylbutylamino, piperazinylpentylamino), a hydroxyalkylamino group (e.g. hydroxyethylamino, hydroxypropylamino, hydroxybutylamino, hydroxypentylamino), an aminoalkyl group (e.g. aminomethyl, aminoethyl, aminopropyl, aminobutyl, aminopentyl), a piperazinylalkyl group (e.g. piperazinylmethyl, piperazinylethyl, piperazinylpropyl, piperazinylbutyl, piperazinylpentyl), a hydroxyalkyl group (e.g. hydroxymethyl, hydroxyethyl, hydroxypropyl, hydroxybutyl, hydroxypentyl), amino group, piperazino group, and hydroxy group.
The alkylene group in the definition (B) formed by combining adjacent two groups of R1, R2, R3, R4 and R5 each other, wherein one or two methylene groups may optionally be replaced by xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94 or xe2x80x94NHxe2x80x94, and one of the carbon atoms of said alkylene group is substituted by a group of the formula: xe2x80x94Xn-Alkm-R6, is formed by combining each other two substituents at 7- and 9-positions, 9- and 10-positions, 10- and 11-positions, or 11- and 12-positions of the formula [I]. Such alkylene group includes a straight chain or branched chain alkylene group having 2 to 6 carbon atoms, for example, ethylene, trimethylene, tetramethylene, pentamethylene, hexamethylene, methylethylene, methyltrimethylene, etc., and the alkylene group wherein a methylene group or two methylene groups thereof are replaced by xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94 or xe2x80x94NHxe2x80x94 are the same ones as those exemplified in the above. Among these alkylene groups, ones wherein one of the carbon atoms is substituted by a group of the formula: xe2x80x94Xn-Alkm-R6 are also the same ones as those exemplified in the above.
The lower alkyl group for the remaining groups of R1, R2, R3, R4 and R5 which do not form an alkylene group includes a straight chain or branched chain alkyl group having 1 to 6 carbon atoms, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, pentyl, hexyl, etc.
The halogen atom is fluorine, chlorine, bromine or iodine.
Moreover, examples of the partial structure formed by Ring A and Ring B in the above definition (A) of the formula [I] are the following structures: 
wherein X, Alk, R6, m and n are the same as defined above.
Besides, examples of the partial structure formed by Ring A and Ring B in the above definition (B) of the formula [I] are the following structures: 
wherein R1, R2, R3, R4 and R5 are each an alkyl group, a halogen atom or a hydrogen atom, and X, Alk, R6, m and n are the same as defined above.
Among them, the preferable combinations of the R1, R2, R3, R4 and R5 are:
(1) R1 and R2 combine to form a trimethylene group, R3 is a 3-aminopropyloxy group, R4 and R5 are each a hydrogen atom: 
(2) R1 is a piperazinomethyl group, R2 and R5 are each a hydrogen atom, R3 and R4 combine to form an ethylenedioxy group: 
(3) R1 is an aminomethyl group, R2 and R5 are each a hydrogen atom, R3 and R4 combine to form an ethylenedioxy group: 
(4) R1, R2, R4 and R5 are each a hydrogen atom, R3 is a 3-aminopropytoxy group: 
(5) R1 and R2 combine to form an amino-substituted trimethylene group, R3 is a methyl group, R4 is a fluorine atom, R5 is a hydrogen atom: 
xe2x80x83and
(6) R1, R3, R4 and R5 are each a hydrogen atom, R2 is an amino group: 
The xe2x80x9cpolysaccharide having carboxyl groupsxe2x80x9d of the present invention includes the same as those as disclosed in the above mentioned WO 94/19376, and includes polysaccharides originally having carboxyl groups in the structure thereof (e.g. hyaluronic acid, pectic acid, alginic acid, chondroitin, heparin, etc.), and polysaccharides having originally no carboxyl group (e.g. pullulan, dextran, mannan, chitin, mannoglucan, chitosan, etc.) but being introduced thereto carboxyl groups. Among these polysaccharides, dextran is especially preferable, particularly dextran having an average molecular weight of 20,000 to 400,000 is more preferable, and particularly dextran having an average molecular weight of 50,000 to 150,000 is most preferable (said average molecular weight being determined by Gel permeation chromatography method (GPC analysis), Shinseikagaku Jikken Koza, vol. 20, p. 7). The polysaccharides originally having no carboxyl group but being introduced thereto carboxyl groups mean ones which are prepared by replacing hydrogen atoms of a part or all of hydroxyl groups of polysaccharides originally having no carboxyl group by a carboxy-C1-4 alkyl group.
The xe2x80x9cpolysaccharide having carboxyl groupsxe2x80x9d of the present invention also includes ones which are prepared by treating a polysaccharide originally having no carboxyl group with a reducing agent, and then followed by replacing hydrogen atoms of a part or all of hydroxyl groups of the product by a carboxy-C1-4 alkyl group.
The alkyl moiety of the above carboxy-C1-4 alkyl group which replaces the hydrogen atoms of a part or all of hydroxyl groups of polysaccharide may be either a straight chain alkyl group or a branched chain alkyl group. Preferable carboxy-C1-4 alkyl group is, for example, carboxymethyl, 1-carboxyethyl, 3-carboxypropyl, 1-methyl-3-carboxypropyl, 2-methyl-3-carboxypropyl, 4-carboxybutyl, etc., and carboxymethyl and 1-carboxyethyl are more preferable.
In the present invention, the polysaccharide having carboxyl groups is preferably a carboxymethylated dextran or pullulan.
When introducing a carboxyalkyl group into polysaccharides, the degree of the introduction thereto is expressed by xe2x80x9cdegree of substitutionxe2x80x9d which is defined by the number of carboxyalkyl groups per a sugar residue, i.e. expressed by the following equation.       Degree of Substitution    =            Number of carboxyalkyl groups in the molecule              Total number of sugar residues in the molecule      
When the carboxyalkyl group is carboxymethyl group, the degree of substitution is occasionally expressed by the degree of carboxymethylation (CM-degree).
When the polysaccharide is pullulan, dextran or mannoglucan, and all of the hydroxy groups thereof are substituted, the degree of substitution thereof is 3, and the preferable degree of substitution is in the range of 0.3 to 0.8.
When the polysaccharide is chitin, and all of the hydroxyl groups thereof are substituted, the degree of substitution thereof is 2, and the preferable degree of substitution is in the range of 0.3 to 0.8.
Besides, it is essential that the polysaccharide of the present invention should have at least one carboxyalkyl group in the molecule except for polysaccharides having originally carboxyl groups. Therefore, polysaccharides having a degree of substitution of 0 should be excluded from the polysaccharide of the present invention.
The polysaccharide having carboxyl groups may be prepared by the method disclosed in WO 94/19376.
The amino acid which intervenes between a camptothecin compound [I] and a polysaccharide having carboxyl groups includes both natural amino acids and synthetic amino acids (including D-amino acid, L-amino acid, a mixture thereof), and also includes either neutral amino acids, basic amino acids or acidic amino acids. Moreover, the amino acid of the present invention may be not only xcex1-amino acids but also xcex2-amino acids, xcex3-amino acids, xcex5-amino acids, etc., and includes, for example, glycine, xcex1-alanine, xcex2-alanine, valine, leucine, isoleucine, serine, threonine, cysteine, methionine, aspartic acid, glutamic acid, lysine, arginine, phenylalanine, tyrosine, histidine, tryptophan, proline, hydroxyproline, xcex3-aminobutyric acid, xcex5-aminocaproic acid, etc.
The peptide of the present invention includes peptides derived from the above amino acids, or peptides having compounds other than amino acids in the part of the chain thereof. For example, a dicarboxylic acid such as succinic acid, a diamine such as ethylenediamine, or a diol such as ethyleneglycol may exist in the middle of the peptide chain or the terminus of the peptide chain. Besides, the binding site of the peptide chain to the carboxyl groups of the polysaccharide usually starts from the N-terminus of the peptide chain through acid-amide bonds. When a basic amino acid (e.g. lysin) exists in the peptide chain, the binding site of the peptide chain may be reversed by binding an xcex5-amino group of the basic amino acid with carboxyl groups of a polysaccharide, and binding an xcex1-amino group with the C-terminus of the peptide chain.
Such peptides may be ones composed of two or more amino acids, i.e. ones having two or more peptide chains, more preferably ones having 2 to 5 peptide chains. Suitable examples of the peptide chain are -Gly-Gly-L- or D-Phe-Gly-(SEQ ID NO:3 or 4 respectively), -Gly-Gly-, -Gly-Gly-Gly-, -Gly-Gly-Gly-Gly-SEQ ID NO:1), -Gly-Gly-Gly-Gly-Gly-(SEQ ID NO:2), -L- or D-Phe-Gly-, -L- or D-Tyr-Gly-, -L- or D-Leu-Gly-, and peptide chains containing these sequences (the N-terminus of these peptides or peptide chains containing these sequences is introduced onto carboxyl groups of a polysaccharide). Among these peptides, -Gly-Gly-L- or D-Phe-Gly-, -Gly-Gly-, -Gly-Gly-Gly-, -Gly-Gly-Gly-Gly-(SEQ ID NO:1), -Gly-Gly-Gly-Gly-Gly-(SEQ ID NO:2), -L- or D-Phe-Gly- and -L- or D-Leu-Gly- are more preferable. Most preferable peptides are -Gly-Gly-L-Phe-Gly-(SEQ ID NO:3), -Gly-Gly-, -Gly-Gly-Gly-, -Gly-Gly-Gly-Gly-(SEQ ID NO:1), and -L- or D-Phe-Gly-.
The camptothecin derivatives of the present invention may usually be prepared by combining the compound [I] with an amino acid or a peptide, followed by reacting the product with a polysaccharide having carboxyl groups.
In the reaction between the compound [I] and an amino acid or a peptide, when R6 of the formula [I] is xe2x80x94NH2 or a piperazino group, the compound [I] is combined with the C-terminal carboxyl group of an amino acid or a peptide through acid-amide bonds. When R6 of the formula [I] is xe2x80x94OH, the compound [I] is combined with the C-terminal carboxyl group of an amino acid or a peptide through ester bonds. In this case, it is preferable to protect other functional groups of an amino acid or a peptide which do not participate in said acid-amide bonds or ester bonds, for example, the N-terminal amino group or other carboxyl groups, are protected in a conventional manner, prior to the reaction of the compound [I] and an amino acid or a peptide. The protecting group may be any protecting groups which are conventionally used for protection of amino acids, and the protecting group of amino group is, for example, t-butoxycarbonyl group, p-methoxybenzyloxycarbonyl group, etc., and the protecting group of carboxyl group is, for example, a lower alkyl group (e.g. t-butyl group), benzyl group, etc.
The production of the above mentioned acid-amide bonds or ester bonds between R6 of the compound [I] and an amino acid or a peptide is carried out by a conventional method, for example, by reacting in the presence of a condensing agent in a suitable solvent. The solvent includes, for example, dimethylformamide, tetrahydrofuran, etc., and the condensing agent includes, for example, dicyclohexylcarbodiimide, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, etc.
The camptothecin compound thus prepared by combining the compound [I] with an amino acid or a peptide, after removing the protecting group of an amino group or a carboxyl group therefrom by a conventional method when an amino group or a carboxyl group thereof is protected, is reacted with a polysaccharide having carboxyl groups, to give the desired camptothecin derivatives of the present invention. In this reaction, a part or all of the carboxyl groups of the polysaccharide are combined with the N-terminal amino group of the amino acid or the peptide which is previously bonded to the camptothecin compound [I], through acid-amide bonds.
The reaction of the camptothecin compound which is produced by combining the compound [I] with an amino acid or a peptide, and a polysaccharide having carboxyl groups is carried out by a conventional method, for example, in the presence of a condensing agent in a suitable solvent. The solvent includes, for example, water, ethanol, dimethylformamide, or a mixture thereof, and the condensing agent includes, for example, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, 2-ethyloxy-1-ethyloxycarbonyl-1,2-dihydroquinoline, etc.
In the camptothecin derivatives of the present invention, the ratio of the polysaccharide and the camptothecin compound [I] which is an active ingredient may be selected according to the kinds of the polysaccharide to be used, but the content of the camptothecin compound [I] in the camptothecin derivative of the present invention is preferably in the following range.
When the polysaccharide is pullulan, dextran, chitin, mannoglucan or N-acetyl-de-N-sulfuric heparin, it is in the range of 0.1 to 20% by weight, more preferably in the range of 2 to 10% by weight.
When dextran is used as a polysaccharide in the present invention, the average molecular weight of the camptothecin derivative of the present invention is preferably in the range of 30,000 to 500,000, more preferably, in the range of 60,000 to 200,000, determined by the GPC analysis.
The camptothecin derivatives of the present invention thus obtained may be converted into a pharmaceutically acceptable salt thereof, if necessary. The pharmaceutically acceptable salt includes, for example, salts with an alkali metal or an alkaline earth metal (e.g. sodium salt, potassium salt, calcium salt, etc.), or salts with an amino acid (e.g. arginine salt, lysine salt, etc.).
Some of the camptothecin compounds of the formula [I] of the present invention are known compounds, for example, compounds disclosed in Japanese Patent First Publication (Kokai) Nos. 279891/1989, 222048/1993, 87746/1994, 228141/1994 and Japanese Patent First Publication (Kohyo) Nos. 503505/1992, 502017/1993, etc., and may be prepared by conventional methods, such as by the method disclosed in the following Reaction Scheme 1: 
wherein R1, R2, R3, R4 and R5 are the same as defined above, R1xe2x80x2, R2xe2x80x2, R3xe2x80x2, R4xe2x80x2 and R5xe2x80x2 are the same as R1, R2, R3, R4 and R5, except that an amino group, a piperazino group or a hydroxyl group in the group of the formula: xe2x80x94Xn-Alkm-R6, which is contained in one of R1xe2x80x2, R2xe2x80x2, R3xe2x80x2, R4xe2x80x2 and R5xe2x80x2 is protected.
That is, the aminocarbonyl compound (1) is condensed with a known pyranoindolidine (2) (cf. EP-0220601-A) by a method known as Friedlxc3xa4nder condensation reaction (cf. Organic Reactions, 28, pp. 37-202, John Wiley and Sons, Inc., New York (1982)), followed by removing the protecting groups from the product to give the camptothecin compound [I].
In the above process, a group of the formula: xe2x80x94Xn-Alkm-R6, which is contained in one of R1xe2x80x2, R2xe2x80x2, R3xe2x80x2, R4xe2x80x2and R5xe2x80x2 may be introduced after said Friedlxc3xa4nder condensation reaction, when m is 1, and n is 1.
That is, in the process of the above Reaction Scheme 1, a compound of the formula (1) wherein a corresponding group to a group of the formula: xe2x80x94Xn-Alkm-R6 is a hydroxyl group (xe2x80x94OH) or an amino group (xe2x80x94NH2) is used, and condensed with the compound (2) by Friedlxc3xa4nder condensation reaction, and the resulting condensed product is reacted with a protected aminoalkanol or hydroxyalkanol represented by the formula: R6xe2x80x2-Alkm-OH (R6xe2x80x2 is a protected amino group, a protected piperazino group, or a protected hydroxy group, and Alk and m are the same as defined above) or a reactive derivative thereof (e.g. a protected aminoalkyl halide, a protected hydroxyalkyl halide), followed by removing the protecting groups therefrom to give the desired camptothecin compound [I].
The starting aminocarbonyl compound (1) may be prepared by the following Reaction Scheme 2: 
wherein R1, R2, R3xe2x80x2, R4 and R5xe2x80x2 are the same as defined above.
The hydroxyl compound (a) is treated with an oxidizing agent such as pyridinium dichromate to give a ketone compound (b), which is further subjected to catalytic reduction in the presence of a suitable catalyst such as palladium-carbon to give the compound (1).
When both m and n are 1, the group of the formula: xe2x80x94Xn-Alkm-R6, which is contained in one of R1xe2x80x2, R2xe2x80x2, R3xe2x80x2, R4xe2x80x2 and R5xe2x80x2, may be introduced into the compound (a) by reacting a compound of the formula (a) wherein a corresponding group to a group of the formula: xe2x80x94Xn-Alkm-R6 is a hydroxyl group (xe2x80x94OH) or an amino group (xe2x80x94NH2) with a compound of the formula: HO-Alk-R6 (Alk and R6 are the same as defined above) or a reactive derivative thereof (e.g. a substituted alkyl halide).
The camptothecin derivatives of the present invention and a pharmaceutically acceptable salt thereof show excellent antitumor activities against various tumors, especially they show excellent therapeutic effects on solid tumors such as pulmonary cancer, uterine cancer, ovarian cancer, breast cancer, gastrointestinal cancer (large bowel cancer, gastric cancer, etc.).
The camptothecin derivatives of the present invention and a pharmaceutically acceptable salt thereof are preferably administered parenterally (e.g. intravascular injection), and are usually used in the form of a liquid preparation (e.g. solution, suspension, emulsion, etc.).
The dosage of the camptothecin derivatives of the present invention varies according to the administration method, ages, weights or conditions of the patients, but it is usually in the range of 0.02-50 mg/kg/day, more preferably in the range of 0.1-10 mg/kg/day, converted into the dose of the camptothecin compound [I] (when R6 is xe2x80x94NH2, a hydrochloride of the camptothecin compound [I], and when R6 is a group of the formula: 
a hydrochloride or dihydrochloride of the camptothecin compound [I]).
The camptothecin derivatives of the present invention and a process for preparing thereof are illustrated in more detail by the following Examples, but should not be construed to be limited thereto.